Fiber coupler fabrication by 4.6 μm quantum cascade laser irradiation

Next-generation free-space optical (FSO) networks rely on wavelength division multiplexing (WDM) and optical emitted powers exceeding 100W to bridge vast inter-satellite distances. Within the optical terminals, routing these intense signals requires ultra-low-loss fiber components to prevent destructive thermal runaway in a vacuum environment. Traditional flame-based fabrication of fused devices (e.g., fiber couplers) introduces hydroxyl (OH^-) impurities that absorb power and compromise reliability, whereas CO₂ laser methods demand complex beam-shaping optics. Here, we introduce a highly stable, contaminant-free fabrication method utilizing a 4.6 μm quantum cascade laser (QCL) diode fusion process. As a proof of concept, we demonstrate a 2×2 fused fiber coupler exhibiting 0.65dB to 0.75dB excess loss across the C-band and a ∼50% coupling ratio at 1550.6nm, providing a highly scalable solution for future high-power space communications.